1. Field of the Invention
The present invention relates to a fuel injection apparatus for supplying fuel from a fuel tank to an internal combustion engine for a vehicle, and more particularly, to a fuel injection apparatus wherein the fuel injection is stopped by a discharging the pressure in a fuel injection nozzle via a spill control valve device.
2. Description of the Related Arts
In a known fuel injection device for an internal combustion engine for a vehicle, the pressure is discharged at a point upstream of a fuel injection nozzle by a spill valve device, to stop a fuel injection operation. A spill valve device provided with a spill valve body and piezoelectric actuator has been proposed in, for example, U.S. Pat. No. 4,643,155 and Japanese Patent Publication No. 61-12109.
In the above-mentioned type of piezoelectric actuator, a drive power therefrom is transmitted to a spill valve body by an amount of fuel used as an operating fluid, whereby a small displacement of the piezoelectric actuator is amplified and transmitted to the spill valve body. Although the operating fluid medium is stored in a sealed oil chamber, unless recharged, the amount of stored operating fluid is gradually depleted over a certain period of operation, and thus the efficiency of the device is lowered. Accordingly, the operating fluid is supplemented via an oil supply passageway. This fuel supplementing passageway connects the sealed chamber to a fuel passageway in which the pressure is higher than a predetermined pressure, i.e., a passageway in which the fuel is charged. The above-mentioned Japanese Patent Publication No. 671-12109 discloses that the delivery outlet of a feed pump for pressurizing the fuel in the fuel tank is connected to the sealed oil chamber via the oil supply passageway, i.e., proposes only a connection of the delivery side of the feed pump to the sealed oil chamber. To produce a practically efficient injection fuel apparatus, the construction must be as simple as possible, and therefore, the following considerations must be taken into account when designing such a fuel passageway. Theree states of pressure exist in a conventional fuel injection apparatus; a low pressure state wherein the pressure in the fuel tank is low, an intermediate pressure state wherein the pressure of the fuel tank is pressurized to a pressure higher than a predetermined value, and a high pressure state wherein the pressure is made much higher than intermediate state pressure by, for example, a pressurizing pump such as a plunger pump. The oil sealed chamber for storing the piezoelectric actuator operating fluid is designed to be connected to a passageway in which the intermediate pressure state prevails, which allows fuel (operating fluid) having a predetermined pressure to be supplied to the chamber. A passageway is provided between the pressurizing pump, in which a high pressure state prevails, and a fuel injection nozzle, for discharging the fuel from the spill chamber to stop the fuel injection when the fuel injection cycle is completed. A fuel having an intermediate pressure is introduced into this spill chamber, in which the intermediate pressure state thus prevails, and the supply passageway usually has an intermediate pressure. Accordingly, a drawback will occur in that the fuel supplementing passageway is open to a very high pressure of the pressurized chamber in the high pressure pump via the passageway through which the fuel is passed.
In the construction of the prior art, if the fuel feeding passageway and the fuel supplementing passageway are connected, a high pressure in the pressure pump or a spill operation as a result of a movement of the spill valve body cause the fuel pressure as spilled to flow to the supplementing fuel passageway, which pressurizes the operating fluid. As a result, the pressure of the operating fluid is increased, and a valve member of the spill valve body, which is operated by the operating fluid, is moved toward the valve seat. Therefore, when commencing a spill operation as a result of a separation of the valve member from the valve seat, the resultant spill pressure is applied to the operating fluid, which moves the valve member toward the valve seat. This reduces the speed of movement of the valve member while opening, and thus the responsitivity of the valve member during the spill operation is decreased.